The present invention relates to heat exchangers in general and more particularly to an improved split resistant tubular heat transfer member through which refrigerant liquid flows and functions to evaporate or to condense, thereby respectively to accept heat from and to provide heat to a coolant fluid which is disposed in contact with the exterior of the tubular member. Yet further, the present invention is directed to a particularized structure for a tubular heat transfer member which provides resistance to splitting during the manufacture thereof, and does so while retaining its beneficial heat exchange characteristics.
The improved split resistant tubular heat transfer member of the present invention is of the variety used in refrigeration and air conditioning systems utilizing an evaporator and condenser. Generally, the evaporator and condenser are comprised of a plurality of parallel tubes connected at the end to form a refrigerant circuit or circuits. A plurality of fins are connected in heat exchange relationship to the tubes and extend transversely of the tubes. In use, refrigerant is condensed in the condenser and evaporated in the evaporator. Liquid or air is passed over the condenser to condense the refrigerant fluid therein. Air passed over the evaporator is cooled. Cooled air from the evaporator may be used to cool the interior of a space, e.g. room to be cooled.
In the above generalized procedure of refrigerating or air conditioning, the physical characteristics of the heat exchange tube determines the heat transfer efficiency. One certain type of heat transfer tubes which have found acceptance in the prior art utilize a multiplicity of rib-like projections, or "fins", disposed on the interior surface of the tube. In such heat transfer apparatus, a thin film layer of refrigerant liquid is maintained in contact with the interior surface of the tube, and in particular is disposed on the surface of the fins and the grooves therebetween. If the tube used in an evaporator application, this thin film layer is the subjected to evaporation. The multiplicity of rib-like fins increases the surface area available for evaporation and accordingly increases the efficiency of such evaporation. In some prior art ribbed tubing structures, the ribs are disposed in a spiral or helical disposition to cause a controlled degree of turbulence in the refrigerant liquid, which diminishes laminar flow and also serves to break up any insulating barrier layer of vapor from forming on the interior surfaces of the tube.
Several prior art patents have made proposals for improvement of interior rib-containing tubular heat transfer members. Those prior art patents include:
U.S. Pat. No. 4,044,797--Fujie PA1 U.S. Pat. No. 4,480,684--Onishi PA1 U.S. Pat. No. 4,545,428--Onishi PA1 U.S. Pat. No. 4,658,892--Shinohara PA1 U.S. Pat. No. 4,938,282--Zohler PA1 U.S. Pat. No. 4,921,042--Zohler PA1 U.S. Pat. No. 4,118,944--Lord, et al.
These and other various tubular members of the prior art, including several different forms of interiorly disposed rib structures have increased somewhat the efficiency of refrigerant operation. However, such tubing has in several particulars been difficult or inefficient of manufacture, and has likewise resulted in a tendency to split the tube during manufacture.
Rifle tube is used in the manufacture of heat transfer devices called "coils". The coils are constructed by placing tubes (aluminum or copper) through holes stamped into thin sheets of aluminum or copper. For assembly purposes the tube must be smaller than the holes in the sheets, but for heat transfer purposes the tube must be in intimate contact with the sheets. To achieve the intimate contact, a ball is forced through the tube after it is inserted into the sheets. The ball causes the OD of the tube to "expand" into intimate contact with the sheets. This is called the "expansion process".
On smooth tube, the expansion process works well and causes few problems. However, with rifle tube the stress caused by the expansion process is increased in the thin part of the tube wall, causing the tube to split if there is even a minimal defect in the tube. It has been found by the applicants herein that, by increasing the amount of wall available (bottom wall to fin wall ratio) to accommodate the required expansion, the likelihood of the tube splitting can be reduced.
In view of the above difficulties, defects and deficiencies of prior art structures, it is a material object of the improved tubular heat transfer member of the present invention to provide a novel structure having increased resistance to splitting during the manufacture thereof, while at the same time retaining the beneficial heat transfer characteristics of interiorly ribbed tubular heat transfer members.
In addition, the improved split resistant tubular heat transfer member of the present invention has the further beneficial characteristic wherein the fins thereof hold their shape better during the expansion process, thus permitting the structure to retain a larger degree of its beneficial heat transfer characteristics after the expansion process than prior art tubing has been able to accomplish heretofore.
It is a further object of the present invention to provide a versatile and novel tubular structure which may be utilized for evaporation and for condensation functions. These and other objects and advantages of the improved split resistant tubular heat transfer member of the present invention will become known by those skilled in the art upon a review of the following summary of the invention, brief description of the drawing, detailed description of preferred embodiments, appended claims and accompanying drawing.